要允许添加新节点，但要防止删除或覆盖任何节点:

To allow adding new nodes, but prevent deleting or overwriting any node:

".write": "!data.exists()"

要允许添加和覆盖(但不能删除)任何节点，

To allow adding and overwriting, but not deleting, any node:

".write": "newData.exists()"

更新:这些规则的模拟器屏幕截图